(rĀʹdē-əm) noun. Symbol RaA rare, brilliant white, luminescent, highly radioactive metallic element found in very small amounts in uranium ores, having 13 isotopes with mass numbers between 213 and 230, of which radium 226 with a half-life of 1,622 years is the most common. It is used in cancer radiotherapy, as a neutron source for some research purposes, and as a constituent of luminescent paints. Atomic number 88; melting point 700°C; boiling point 1,737°C; valence 2, radium.
radium therapy (rĀʹdē-əm thĕrʹə-pē) noun. The use of radium in radiotherapy, especially in treating cancer, terapi radium.